Coherent Turbulent Structures Across a Vegetation Discontinuity

The study of turbulent flow across a vegetation discontinuity is of significant interest as such landscape features are common, and as there is no available theory to describe this regime adequately. We have simulated the three-dimensional dynamics of the airflow across a discontinuity between a forest (with a leaf area index of 4) and a clearing surface using large-eddy simulation. The properties of the bulk flow, as well as the large-scale coherent turbulent structures across the forest-to-clearing transition and the clearing-to-forest transition, are systematically explored. The vertical transport of the bulk flow upstream of the leading edge gives rise to the enhanced gust zone around the canopy top, while the transport downstream of the trailing edge leads to the formation of a recirculation zone above the clearing surface. The large-scale coherent structures across the two transitions exhibit both similarities with and differences from those upstream of the corresponding transition. For example, the ejection motion is dominant over the sweep motion in most of the region 1